Anomalous attenuation of extraordinary waves in the ionosphere heating experiments

Multiple scattering of radio waves by artificial random irregularities HF-induced in the ionosphere F region may cause significant attenuation of both ordinary and extraordinary waves together with common anomalous absorption of ordinary waves due to their non-linear conversion into plasma waves. To demonstrate existence and strength of this effect, direct measurements of attenuation of both powerful pump wave and weak probing waves of extraordinary polarization have been carried out during an experimental campaign on September 6, 7 and 9, 1999 at the Sura heating facility. The attenuation magnitude of extraordinary waves reaches of 1-10 dB over a background attenuation caused by natural irregularities. It is interpreted in the paper on the base of the theory of multiple scattering from the artificial random irregularities with characteristic scale lengths of 0.1-1 km. Simple procedure for determining of irregularity spectrum parameters from the measured attenuation of extraordinary waves has been implemented and some conclusions about the artificial irregularity formation have been obtained.Comment: 17 pages, 9 figure

The Radiation Transfer at a Layer of Magnetized Plasma With Random Irregularities

The problem of radio wave reflection from an optically thick plane monotonous layer of magnetized plasma is considered at present work. The plasma electron density irregularities are described by spatial spectrum of an arbitrary form. The small-angle scattering approximation in the invariant ray coordinates is suggested for analytical investigation of the radiation transfer equation. The approximated solution describing spatial-and-angular distribution of radiation reflected from a plasma layer has been obtained. The obtained solution has been investigated numerically for the case of the ionospheric radio wave propagation. Two effects are the consequence of multiple scattering: change of the reflected signal intensity and anomalous refraction.Comment: 22 pages, 4 figure

Ultrastructure of oocytes and female copulatory organs of Acoela

The ultrastructure of oocytes in four species of Acoela ( Archaphanostoma agile, Otocelis rubropunctata, Symsagittifera japonica, and Amphiscolops sp.) and that of female copulatory organs of S. japonica and Amphiscolops sp. are described for the first time. According to the similarity of the reproductive apparatus structure, the sister relationships between the families Sagittiferidae and Convolutidae are confirmed. The ultrastructure of oocytes and specific features of oogenesis are proposed to be useful in phylogenetics of Acoela

Ultrastructure of oocytes and female copulatory organs of Acoela

© 2014, Pleiades Publishing, Inc. The ultrastructure of oocytes in four Acoela species representing different families (Archaphanostoma agile, Otocelis rubropunctata, Symsagittifera japonica, and Amphiscolops sp.) and of female copulatory organs (bursae) in S. japonica and Amphiscolops sp. is described for the first time. The sister relationship between the families Sagittiferidae and Convolutidae is confirmed by the similarity of their reproductive apparatus structure. It is suggested the ultrastructure of oocytes and specific features of oogenesis can be used in the phylogenetics of Acoela

Interferometry of infragravity waves off New Zealand

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 1103-1122, doi:10.1002/2013JC009395.Wave interferometry is a remote sensing technique, which is increasingly employed in helioseismology, seismology, and acoustics to retrieve parameters of the propagation medium from two-point cross-correlation functions of random wavefields. Here we apply interferometry to yearlong records of seafloor pressure at 28 locations off New Zealand's South Island to investigate propagation and directivity properties of infragravity waves away from shore. A compressed cross-correlation function technique is proposed to make the interferometry of dispersive waves more robust, decrease the necessary noise averaging time, and simplify retrieval of quantitative information from noise cross correlations. The emergence of deterministic wave arrivals from cross correlations of random wavefields is observed up to the maximum range of 692 km between the pressure sensors in the array. Free, linear waves with a strongly anisotropic distribution of power flux density are found to be dominant in the infragravity wavefield. Lowest-frequency components of the infragravity wavefield are largely isotropic. The anisotropy has its maximum in the middle of the spectral band and decreases at the high-frequency end of the spectrum. Highest anisotropy peaks correspond to waves coming from portions of the New Zealand's shoreline. Significant contributions are also observed from waves propagating along the coastline and probably coming from powerful sources in the northeast Pacific. Infragravity wave directivity is markedly different to the east and to the west of the South Island. The northwest coast of the South Island is found to be a net source of the infragravity wave energy.The collection of DPG data was supported by the National Science Foundation Continental Dynamics program under grants EAR-0409564, EAR-0409609, and EAR-0409835. This work was supported, in part, by the University of Colorado Seed Grant ‘‘Study of Ocean Infragravity Waves with a Large Array of Seafloor Seismometers,’’ the National Science Foundation award OCE 1129524, and the Office of Naval Research award N00014-13-1–0348.2014-08-1